1. Field of the Invention
The invention relates to an active matrix liquid crystal display device, and more particularly to an active matrix liquid crystal display device and a driving method thereof for increasing a visual angle.
2. Description of the Related Art
An active matrix liquid crystal display device is a liquid crystal display device controlling light transmittance of liquid crystal material to display images.
FIG. 4 shows a schematic illustrating an active matrix liquid crystal display device. The active matrix liquid crystal display device comprises a liquid crystal display panel 1 with a plurality of pixels disposed in a matrix for displaying images, a gate driver 2 and a source driver 3 both for controlling the driving of the liquid crystal display panel 1, and a signal processing circuit 4 for receiving an image signal to be displayed and outputting the control signals and display data to the gate driver 2 and the source driver 3.
A plurality of pixel electrodes 40 are disposed in a matrix in rows and columns. A scan signal line 41 (or named a gate line) is used to select the pixels disposed in the same row according to control of the gate driver 2. A data signal line 42 (or named a drain line) is used to provide the voltages corresponding to data to be displayed to the pixels disposed in the same column according to control of the source driver 3. A switching on/off device 43 is used to provide the data of the data signal line 42 to a pixel of a liquid crystal unit according to the scan signal, which may be a thin film transistor (TFT). An opposite electrode 44 is used to provide a common voltage for each liquid crystal unit. A liquid crystal unit coupled between the pixel electrode 40 and the opposite electrode 44 is referred to as a pixel.
The liquid crystal unit uses the voltages applied to the pixel electrode 40 and the opposite electrode 44 to achieve a shutter function for adjusting light quantity. The pixels are regularly divided into the RGB, and a color image composed of RGB lights is projected when a color filter of the RGB is disposed near to the opposite electrode 44. A part corresponding to the RGB pixel array is referred to as a sub-pixel.
By applying a voltage signal to each sub-pixel, the brightness corresponding to the applied voltage is displayed. FIG. 5 and FIG. 6 show the gamma curve diagrams between the voltage of the voltage signal and the brightness. The curve indicates a gamma curve which is obtained by viewing the display in front of the liquid crystal panel. However, the brightness of the pixel for the liquid crystal display depends on the visual angle. So, a gamma curve which is obtained by watching the liquid crystal panel from a side angle is different than an ideal gamma curve in reality, thus displaying an obscure image for a viewer.
Therefore, the method shown in FIG. 5 and FIG. 6 is used to divide each sub-pixel into two parts which separately provide two different voltage signals according to the curve b and curve c, such that the average brightness obtained by viewing the liquid crystal panel from a side angle may form the ideal gamma curve a, thus reducing dependence on the visual angle. Other than the situations shown in FIG. 5 and FIG. 6, the two signals may be the combinations of other signals.
However, if each sub-pixel is divided into two parts to provide two different voltage signals, respectively, the source and gate lines must be increased, thus causing decrease in aperture rate for the liquid crystal panel.